Every successive generation of integrated circuits brings smaller devices to increase device density and speed. However, as integrated circuit devices get smaller, the signal delay due to resistive-capacitive (RC) effects becomes more pronounced. This delay can be reduced by decreasing either the resistance of the wiring, or by reducing the capacitance of the interlayer insulating layer. To reduce resistance, aluminum wiring has been replaced with copper in many conventional devices. However, it has been difficult to reduce the capacitance of the interlayer insulating layer used with copper interconnects.